I was recently asked by a dear Irish brother for a plan of reading when it came to the works of Andrew Fuller. The following is what I suggested.
Without being self-serving, I hope, begin with the Armies of the Lamb. There is nothing like getting into a figure by reading his letters.
Then I would suggest his circular letters, those written for the Northants Association, in chronological order. These give you some idea of Fuller the churchman in the midst of connectional links and associational network of friends and fellow pastors.
Then read some of his sermons, esp. the ones on the ministry, justification, and soteriological issues.
His Gospel Worthy of All Acceptation is his most important controversial work. After it, read his Letters on Sandemanianism.
Finally, read his Memoirs of Pearce. What he includes in that work says so much about his piety.